The mammalian metabolism of R‐(‐)‐m‐synephrine

Abstract

The metabolism of R‐(‐)‐m‐synephrine (administered orally and by inhalation in man and intraperitoneally in rats) was studied quantitatively by a gas chromatography‐mass spectrometry‐selected ion monitoring (g.c.–m.s.–s.i.m.) method using deuterated internal standards. When m‐synephrine hydrochloride was administered orally to humans in normal dosage regimens four main metabolites were excreted in urine: (i) unconjugated m‐hydroxymandelic acid (MHMA, 30%), (ii) m‐hydroxyphenylglycol (MHPG) sulphate (6%), (iii) m‐synephrine sulphate (47%) and (iv) m‐synephrine glucuronide (12%). The comparable figures after inhalation of the drug were 24, 6, 56 and 5%. Intraperitoneal injection of m‐synephrine into rats gave: unconjugated MHMA (5%), MHPG sulphate (35%), unconjugated m‐synephrine (7%) and conjugates of m‐synephrine (9%:4% as the glucuronide and 5% as the sulphate). Copyright © 1983, Wiley Blackwell. All rights reserved